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IIIIII I NWu United States Patent 3,503,048 ARRANGEMENT IN COMPUTERS FOR CONTROL- LING A PLANT CONSISTING OF A PLURALITY 0F COOPERATING MEANS Oleg Avsan, Huddinge, Goran Anders Henrik Hemdal, Tyreso, Torbjorn Konrad Johnson, Alvsjo, Lars-Olaf Noren, Huddinge, and Ake Bertil Fredrik Svensson, Hagersten, Sweden, assignors to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Filed Feb. 23, 1967, Ser. No. 618,193 Claims priority, application Sweden, Mar. 25, 1966, 3,972/ 66 Int. Cl. G02b 27/14 US. Cl. 340172.5 3 Claims ABSTRACT OF THE DISCLOSURE A telephone system is controlled by a system of redundant pairs of computers. Each computer comprises a central processing unit, an instruction memory unit, a working memory unit and a transfer unit for interfacing with the telephone system. The units are only temporarily assigned to cooperate with each other to form the computers and can be arbitrarily switched to different configurations under a supervisory program. Each pair of computers can perform the entire program sequence of control but each pair is assigned a different section of the program sequence. If faults are detected when one pair of computers is performing its section, another pair is automatically assigned to take over.

The present invention concerns a computer arrangement for controlling a system of plant consisting of a plurality of cooperating means, eg an automatic telecommunication plant including central units for carrying out calculation operations, memory units for the storing of instructions, and memory units for storing of information during the carrying out of the calculation operations. These units co-operate with each other in such a way that each one of the mentioned units, in cooperation with one unit of the remaining categories, forms a computer so that the computers formed in this way, by means of at least one transfer unit on the one hand detects the state of the different means of the telecommunication plant and on the other hand operates these means with the guidance of the result received from the computers.

In a computer controlled plant, e.g. an automatic telecommunication plant where one computer is not sufficient to carry out the tasks in a satisfying way a conceivable solution is that a number of cooperating computers corresponding to the required traffic handling capacity is used, the plant being divided into independent subunits which are served each by its own computer. In establishing a connection between two different means associated with independent subunits in such an arrangement it is, however, necessary to carry out a number of information exchanges and comparisons between the calculation results of the respective computers in order to permit the selection and the establishing of a connection between said two means. This involves, consequently, an additional load on the computers and the plant will function as a plant consisting of a number of different independent telecommunication exchanges. A further consequence will be that for the same traffic volume a greater number of means will be necessary than in a telecommunication exchange which works as one unit.

An object of the invention is to eliminate the mentioned inconvenience and to divide up the work between till ice

the computers in a telecommunication plant consisting of a plurality of computers in such a way that every computer carries out certain definite functions for the whole plant so that the information exchange between the different computer is simplified to a great extent.

The arrangement for controlling a plant, eg, an automatic telecommunication plant, is in the main characterized in that it includes means by means of which every unit of the arrangement can receive information from a plurality of units alternatingly so that the momentarily cooperating units form computers existing only during the time of cooperation while at another time a unit included in such a computer together with other units forms another momentarily existing computer.

According to another characteristic of the invention the instruction memory associated with each one of the computers is arranged for storing all the instructions by means of which a computer can carry out all the functions necessary for controlling the plant but the work between the different computers is divided up in such a way that certain sections of the whole instruction sequence are carried out by one definite computer, Associated with every computer is an indicating memory field from which the respective computer, after carrying out every section of instructions, fetches information concerning the address of the section which shall be carried out next. There is also associated with every computer a memory field with a sequence of supervisory instructions by means of which a computer, upon the receiving of an information implying that a state of operation exists which is defined as anomalous (e.g. fault of circuit, overload), can erase at least one section address in the indicating memory field for a computer which produced the information concerning the fault and can as necessary write this section address into the indicating memory field of another arbitrary computer.

The invention will be explained more in detail with reference to the accompanying drawing in which FIG. I is a block diagram of a system for controlling an automatic telecommunication plant according to the invention, FIG. 2 is a block diagram of a computer formed by the units included in the system, FIG. 3 shows diagrammatically the control unit of one of the central units included in the system, FIGS. 4a and 4!) show the cooperation between the units included in the system, FIG. 5 shows diagrammatically how the sequence order between the different units is obtained, FIG. 6 shows diagrammatically the cooperation between the working lists and control programs of the computers, FIG. 7 shows diagrammatically the function of the computer supervisory program, FIG. 8 shows diagrammatically the work distribution between the different priority levels, at an arbitrary moment, FIG. 9 shows diagrammatically the function of the computer supervisory program in connection with the clock controlled interruption, FIG. 10 shows diagrammatically the function of the system supervisory program upon overload, FIG. 11 shows diagrammatically the function of the system supervisory program upon transporting the work of one computer to another one, FIG. 12 shows the function of the system supervisory program upon a fault in a data memory unit. and FIG. 13 shows the function of the system supervisory program upon transporting a part of the work of one of the computers to another computer.

In FIG. 1 there is shown a telephone plant TA which is controlled by means of a computer system. This system includes a number of central units CE (central processing units), instruction memories IM (instruction memory units), data memories DM (working memory units) and transfer units FE which can feed information to and receive information from each other as symbolically indi- 3 cated by a connection network KN. The number of units is not necessarily the same in the respective groups. In this way a central unit CE, e.g., at a definite time can feed information to and receive information from a definite data memory DMl while at another time it can feed information to and receive information from another data memory DM2. The momentarily cooperating units can be regarded to form a computer during the time of cooperation but at another time one or more of the mentioned units can be part of another computer as will be explained in the following. As a principle an arbitrary unit should be able to cooperate with an arbitrary unit but according to the embodiment it is supposed that a definite instruction memory IM as a rule cooperates with a definite central unit CE and for the sake of simplicity is called together with this unit a calculation unit D. All the units, the calculation units Dl-D3 as well as the memory units DM1-DM3 are suitably doubled and work in parallel to obtain an effective control and operation stability, the result obtained from the parallelly working units being continuously compared in order to determine in known manner upon a deviation that a fault exists. In regard to the fact that the functions of the doubled units are identical for the sake of simplicity e.g. DIA and B1B are not mentioned individually in the following but only D1 and similarly not DMZA and DMZB but only DMZ. If, consequently, it is mentioned that, e.g., the calculation unit D2 and the data memory DMI momentarily form a computer two parallelly working computers are concerned. In these computers the instruction memory 1M contains the instruction list or the instruction sequences, the central unit CE carries out the calculation operations ordered by the instructions and the data memory DM stores temporarily the information necessary for the carrying out of the calculation operations in a way known per se.

The computers for ed in the described way receive information concernin the identity of the subscribers and of the switching means together with the information about their busy or idle condition in the form of binary words. In accordance with this information they select a switching path in which all the switching means are idle and operate thereafter all the means included in the switching path by sending control orders in the form of binary words. Thus there are on the one hand binary information words concerning, e.g., the condition of the lines and relays which words are fed to the calculation units and on the other hand binary information words which words are fed from the calculation units to the telephone exchange to operate the switching means. This can take place in both directions in the form of, e.g., 16 digit binary words.

The telephone plant TA can be of an arbitrary type. It includes, according to FIG. 1 a switching network SLGV to which a number of lines L1, L2 and subscribers Abl, Ab2 respectively are connectable via line equipment LU. Connection between the different lines and subscribers respectively takes place by means of connection means with different functions, e.g., link circuit relay sets SNR for connection of local calls, tone senders TS for sending tone frequency signals to the subscribers, code receivers KM for receiving digit signals, code senders KS for sending digit selecting signals to a code receiver in another exchange, incoming line repeaters FIR and outgoing line repeaters FUR.

Because of the great difference in operating speed of the computers with which the binary words are produced which operate the switching means and the operating speed of relays and selectors transfer means FEI-FE3 are necessary which store the information received from the computers until the more slowly operating means have been activated and which store the condition information received from the telephone plant until this information is fed to the computer as it will be described later on. The binary words which contain information concerning the condition of the switching means and the binary words which contain information with respect to which switching means are to be operated, respectively, do not necessarily concern individual means but can concern groups of means (subscribers equipments, selectors, etc.), according to the embodiment 16 means, in which Words the idle condition of a means is represented, e.g. by binary 0 while the occupied state is represented by binary 1. In a similar way binary 1 can signify that the switching means which corresponds to the respective digit position in the word received from the computer is to be operated while those means the corresponding digit position of which is binary 0 shall not be operated in the respective l6-group. To be able to find the 16- group from which a test instruction shall be received and to which an operation instruction shall be sent, respectively, an address information is necessary, for which purpose likewise a word containing 16 binary digits is used.

To be able to carry out both functions, i.e., to cooperate with the relatively slow electromechanical switching means in the telecommunication plant as well as with the considerably faster computer units, the transfer units FE1-FE3 have two buffer registers; an address register FA and a result register FR which registers can store the high speed information received from the computers and retransport it to those parts which operate the relays and the selectors. This is shown in FIG. 1 as the transfer units FEIFE3. Of safety purpose even the transfer units are doubled. The address register PA as well as the result register PR in each one of the transfer units can each, via its l6-wire conductor via the switching network KN, be connected to one or another of the computers. The first mentioned register receives from this computer the calculated address in the form of a l6-digit binary word and the last mentioned register receives from the computer the calculated operation information in the form of a 16-digit binary word or alternatively receives from the transfer unit information about the condition detected in the telephone plant. SMR indicates fast relay operation units which store the information words received in rapid sequence from the computer unit via the result register FR until these information words have operated, e.g., relays or selectors. VMR indicates a selector operating relay set, and RMR indicates a relay operating relay set which both receive their operating signals from unit SMR. Even those means send leave information to their computer concerning the state: a line test device LT, a selector test device VT and relay test devices RT1, RTZ. These three last mentioned types of means do not need an transfer means in the direction of the computer due to the difference in operating speed since the sensing can take place in the speed determined by the computer. The transfer unit includes a decoding device A0 which converts the binary address information received from the computer to positional information.

The functions of the telephone plant can be divided in such a way that the calculation units D1D3, or more ex actly the computers temporarily formed of those and of the data memories DMl-DMS, are utilized in about the same degree. According to the embodiment, it is assumed that the calculation unit D1 carries out the sensing of lines to determine the state of the lines by means of the line test device LT, operation of the selectors by means of the selector operating device VMR and the operating of certain slow relays by means of the relay o eration unit RMR. The calculation unit D2 carries out the sensing of the state of the selectors by means of the selector test device VT, it operates certain relay functions by means of the relay operation units RMR and detects the state of a number of relays by means of the units RT1, RTZ. The calculation unit D3 carries out the receiving. analysis and sending of digits by means of the units RT1 and SMR. It should be pointed out that all the transfer units normally carry out the same functions but to make the description more clear it has been assumed in FIG. 1 that the transfer units FEIA, FEIB FE3B are substantially specialized in certain functions which correspond to the functions of the calculation units.

To explain the function of the system a concise description is first made of a computer unit formed by a calculation unit D, a data memery DM and a transfer unit FE for performing the operations necessary for controlling an automatic telephone exchange and which computer unit is not shown in its doubled or redundant form for the sake of clarity. As mentioned above the calculation unit D includes on the one hand a central unit'CE which in its turn includes a number of registers RA, RB, RC, a logical unit LE and a control unit SE for a microprogram (see FIG. 2), on the other hand the instruction memory IM in which the instructions to be carried out by the computer are stored, each, in its definite address in the form of, e.g., I6-digit binary Words. These instructions are read out sequentially or in another sequence prescribed by the program and each instruction implies the carrying out of a number of definite operations which are associated with this instruction and are determined by the microprogram of the computer. The microprogram can imply reading out and writing of information in the different means, transport of information from one means to another one, carrying out of logical operations in the logical unit, etc., in a sequence and in a number of stages defined by the special instruction. Associated with the instruction memory IM is an address register IA in which the address is written in which the intended instruction is to be found in the instruction memory, and an instruction register IR to which an instruction, selected by means of the address register IA, can be transferred from the instruction memory for forwarding to the remaining means. Alternatively an instruction can be fed from an outer means to the instruction register IR and simultaneously an address into which the instruction shall be located in the instruction memory IM is fed to the address register IA. The last mentioned process does normally not take place during the normal function of the computer but only upon a change of the program while during the normal operation only reading out takes place. The possibility of writing as well as reading out is symbolized by the letters S and L in the block diagram in FIG. 2.

In FIG. 2 only one transfer unit FE and one data memory DM are indicated although, as it has been mentioned above and as it will be described later on, every calculation unit can alternatingly cooperate with different transfer units and data memories in a system according to the invention.

The central unit CE includes according to the embodiment three registers RA, RB, RC (FIG. 2) into each of which a 16 digit binary word can be written, be stored there and fed out from there. An essential part is the logical unit LE which can carry out different arithmetic operations, e.g. addition, subtraction, comparison, logic exclusive or-functions. The logical unit LE is supplied by an input register AA and a result register AR for the recording of one of two operands. the result of addition or subtraction being obtained in the result register in such a way that the binary word written into the last mentioned register is changed to the calculation result. At logical comparison operations an indication is obtained from an indicator, e.g. an indicating flip-flop which upon conformity indicates O while upon deviation indicates 1. Furthermore there is a bit address register LB which in case of an inequality upon comparison between two l6-digit binary words indicates the digit position for, e.g., the lowest digit position in which an inequality has occurred.

A further essential part of the central unit is the control unit SE which determines the transferring of the information between the different registers, in other words the microprogram which for every information word, by means of fixed connections, is determined in the control unit. This unit has an order register OR into which an order is written from the instruction register IR. The control unit decodes the binary word which has been written to the order register, in which binary word, e.g., four bits indicate 16 possible operations, so that one of 16 conductors is activated, compare FIG. 3. The conductor selected in this way determines, together with a number of conductors which are activated sequentially, the feeding in and feeding out of information to and from the registers and the logic operations to be performed by the logical unit respectively, as it will be described below in connection with an example. All the registers can be connected to a common 16-wire conductor (transfer bus) which in FIG. 2 is symbolized by one single conductor, over and-circuits OKl-OKZZ the other input conditions of which are determined by the outputs of the control unit SE. As mentioned above the selected outputs are activated sequentially so that sequentially at least two and-circuits are opened simultaneously to make possible, on the one hand the feeding out of a l6-digit binary word to the common conductors, and on the other hand the feeding of this word to the one of the registers whose input circuit is open. As indicated in FIG. 2 part of the registers have both input and output gates through which access to the registers shall take place while part of th registers are supplied with only input gates from the common l6-wire conductor, as their contents are not fed directly to the common conductors. The function of the control unit SE and the whole simplified computer is easiest to understand in connection with an elementary operation carried out by the computer when it solves a task occurring in connection with the control of an automatic telephone exchange.

One of the many tasks which occur in a telephone plant is to establish whether a change in the state of a definite subscribers line has taken place, i.e., that a subscriber which upon the last test of the state was found to be idle is now occupied or that he has become idle after earlier having been occupied. As it has been pointed out in connection with the transfer unit FE the sensing of the state of the subscribers lines occurs in groups of 16 subscribers so that a l6-digit binary word is obtained in which to each of the 16 subscribers in the group belongs a binary digit 0 or 1 depending on their idle or occupied state, respectively. Selection of a l6-group takes place by means of an address written in the address register FA of the transfer unit PB. The sensing of the state of the subscribers lines occurs cyclically with intervals of, e.g., 300 ms. and the result is written into the data memory DM on the address associated with the respective 16- group, so that the information concerning the last sensing is always stored in the data memory. To establish whether any change in the line state has occurred, a comparison must be carried out between the result obtained in the transfer unit by means of a definite address and the information being found on the corresponding address in the data memory. This comparison can be expressed in the following way: compare the content of register FR with the content of register DR. As it will be explained later the last stage in every operation implies that the next instruction is written into the order register register OR. It is assumed that the instruction written in OR prescribes a comparison between the contents of unit FE and unit DM on an address indicated by the writing order. FIG. 3 shows diagrammatically the control unit SE together with the order register OR into which the instruction order is written in code form. By way of example the first four hits of the characters indicate one of 16 possible operations (the comparison operation corresponding to the code 0100, i.e. 2), the digit positions 5-8 from the left indicate the code 1001, i.e. 9 for the register DR in which one of the operands is to be found according to the embodiment, the digit positions 912 from the left indicate the code 1011, i.e. 11 for the register FR in which the other operand is to be found according to the embodiment. According to the made simplification the digit positions 13-16 indicate the address of the 16-group of subscribers to be tested and which, according to the example, has been assumed to have the address 7. In reality the order register contains only the address of that one of the registers in the logical unit, which in its turn contains the 16 bits address of the respective l6-group of subscribers. Thus the instruction word is written 0010 1001 1011 0111.

The control unit SE is provided with decoders AVKl, AVKZ and AVK3 each one with four inputs and 16 outputs with only one being activated in every decoder: the output No. 2 of the decoder AVKI indicating that the operation is a comparison, the output No. 9 of the decoder AVK2 indicating that it concerns the register DR with the code No. 9 and the output of No. 11 of the decoder AVK3 indicating that it concerns the register FR with the code No. 11. By EK is indicated a stepping forward chain with a number of outputs which are activated sequentially one after the other and which together with the output No. 2 from the decoder AVKl sequentially activate a number of and-circuits Klb, K2b, etc. These and-circuits determine, together with possible signals from the decoders AVKZ and AVK3 which of the and-circuits shall be opened so that the desired transfer of binary words from one register to another can take place and which arithmetic operations shall be carried out in logical unit LE. The first stage is that the instruction word from the order register shall be transferred to address register DA as well as to address FA. This can be expressed as (DA)=(OR) and (FA)=(OR) respectively and takes place in order to make it possible that the digit positions 13-16 from the left can be used as an address for the subscriber's group to be examined. The gates OK22 X13 and 0X19 are opened and simultaneously reading out takes place in unit FE as well as in memory DM, so that the state record concerning the intended subscribers group with the address 7 (0111) is written into register FR as well as into DR. This is carried out by activating the conductor hlb in FIG. 3. The next stage is the transport of the contents of register DR to the register AA in order to prepare the comparison operation by opening the gates 0K9 and OKlZ. This occurs by means of an and-circuit Ka the activating of which depends on the fact that it receives a signal from the conductor h2b of the stepping forward chain EK as well as from the conductor v9a of the decoder AVKZ (corresponding to the code number 9 for the register DR). This can be written: (AA)=(DR). Then the contents of register ER is transferred to register AR, which can be written: (AR)=(FR). For this purpose the gates OK18 and OK14 must be opened and this occurs by means of an and-circuit Kb which is activated depnding on simultaneously appearing signals on the conductor h3b and the conductor vllb of the decoder AVK3 (corresponding to the code number 11 for register FR). The next stage is a comparison between the contents of register AA and register AR, which is controlled by the next stage of the chain EK via the conductor h4b in such a way that an input In3 of the logical unit LE, which controls the comparison function, is activated.

The logical unit is of a type known per se in which the two operands are fed in the form of 16 digit binary words to the registers AA and AR. These registers differ in that in the first mentioned one every newly entered word erases the already recorded word While in the last mentioned register every newly entered word is added to the already recorded word in the register. In register AR both feeding in and feeding out of the existing word in the register can take place while the register AA only is intended for feeding in from and not for feeding out to other means. By activating the different inputs Inl, D12, 1113 by means of signals from the control unit SE different operations are controlled. By activating, e.g., the input Inl the digit 1 is added to the binary word written in the register AA and the result is written in the register AR. By activating the input I112 the contents of AA and AR are added and the result is written in register AR. If the input I113 is activated, a logical comparison takes place between the contents of registers AA and AR and if any difference in any of the binary character elements exists I is indicated by an indicating flip-flop SEF and upon identity between all the character elements 0" is indicated by the flipflop. The address of the character element with, e.g., the lowest digit position in which deviation has been found, is indicated simultaneously by means of a bit address register LB which has four digit positions and consequently can indicate one of the 16 digit positions.

If upon the above mentioned comparison between the contents of registers AA and AR a deviation has been found in any of the digit positions this is indicated by the l"-position of th indicating flip-flop SEF. If there is no deviation the flip-flop is in the (V-position. For the next step of the stepping forward chain, when this activates the conductor hSb, there are two alternatives (compare FIG. 3) and the next instruction can be fetched from two different places: if a deviation has been found, i.e. the comparison result from flip-flop SEF is 1," the address of the next instruction will be the following in the sequence. The address of the instruction just carried out is stored in the register RC (the reason for this will be understood from the continued operation) and this address must be increased by one. First the gates OK21 and OK12 are opened in order to carry out a transfer of the contents of register RC to register AA, which takes place during the next stage of the stepping forward chain EK by activating the conductor 1161). Thereafter the conductor [17b is activated in order to activate the input Inl of the logical unit LE and add one to the contents of register AA and the result is stored in register AR. From register AR the new address is transferred to register RC for storing by activating the conductor 11% and the gates OKlS and OK20 are opened. From register RC the new instruction address is transferred to address register IA by opening the gates OK21 and 0K7 and reading out takes place, the instruction with the indicated address being transferred to register IR. Then the gates 0K2 and OK16 are opened so that the instruction is transferred to register OR, thus the instruction written earlier in register OR is erased, the stepping forward chain EK is restored to its initial position and a new operation can begin. Thus the position corresponds to the initial stage of the operation just described: on the one hand the instruction is written in the order register OR, and on the other hand the instruction address is written in the register RC.

The new instruction written in the order register is a consequence of th fact that a deviation has been found upon comparison and can imply, e.g., that a connecting process to the respective subscribers equipment is to be initiated. If, on the other hand, no deviation has been found upon comparison and fiipfiop SEF indicates 0, another instruction must be carried out implying that, e.g., the l6-group of subscribers which is the following in the sequence, is to be tested. The address of the tested subscriber's group was written in the digit positions 13-16 from the left. This address must now be increased by one to obtain the address of the following subscribers group. As a consequence of the fact that flip-flop SEF indicates 0" a current path is activated which, in the same way as described in connection with the first alternative, together with the outputs of the stepping forward chain activates the and-circuits K60, K70, etc. (compare FIG. 3) so that signals are obtained sequentially on the outputs Me, 1170, etc. In order to calculate the new address the contents of the order register OR must first be transferred to register AA and this is obtained by opening the gates OK22 and OK12. During the next stage one is added in unit LE to the address part of the word recorded in register AA, i.e. the digit positions 13-16, which occurs by activating a special input InS of the logical unit. In regard to the fact that it is the same instruction which continues with the only difference that the address existing in the instruction word has been increased by one it is not necessary to use the instruction memory IM but the contents of the result register AR can be transferred directly to the order register OR, which takes place by opening the gates OKlS and OK16 by means of the conductor h8c. In this way the same situation has occurred as when the previous instruction was initiated, the stepping forward chain is set to zero and its outputs start again sequentially to activate the conductors hlb, 1121), etc. until equality or inequality has been found between the present and the earlier recorded state of the selected subscribers group.

As a next step to illustrate the function of the arrangement a switching process is briefiy described in which all the calculation units Dl-D3 and data memories DMl- DM3 of the arrangement cooperate with each other. The described operation constitutes only a part of the whole operation of the establishing of a telephone call since the whole operation would be too complicated to describe and would not appreciably contribute to the understanding of the function. As already mentioned the incoming telephone lines are divided u into 16-groups which are continuously sensed, and a comparison takes place between the 16-digit binary word which represents the momentary state of the line group and the lo-digit binary word which represents the earlier state of the line group which is written in the data memory. It is assumed that this task is carried out by the calculation unit D1 which together with the data memory DMl forms a computer for carrying out this task. Such a computer works in the same way as described in connection with the FIGS. 2 and 3. At first, there is sent from the order register OR of the central unit CE in the calculation unit D1 the address indicating the l6-group of subscribers to be tested to the address register FA of the transfer unit Hit. The mentioned address transfer takes place on one hand from the calculation unit DlA to the transfer unit FElA by operating the contact 3/1, and on the other hand from the calculation unit DlB to the transfer unit FElB by operating the contact 4/2 since, as mentioned earlier, all the units are doubled and work in parallel. For the sake of simplicity only the function of the calculation units DlA, D2A, D3A, the data memories DMlA, DMZA, DM3A and the transfer units FEIA, FEZA, FESA will be described. The address written in the address register PA is decoded in the decoder A of the transfer unit FBI to cause the line test unit LT (whose task is to sense physically the voltage state of all the l6-groups of conductors and to represent these in the form of readable 16-digit binary words) to select the 16-digit word corresponding to the actual subscribers group for transfer to the result register FR. In the mentioned word a closed subscribers loop is represented, e.g., by 1 while an open subscribers loop is represented by 0. Simultaneously with the sending of the address to transfer unit FEl it is also sent to the address register DA of data memory DMlA over the contact 1/1 in consequence of which in data memory DMlA there is selected and transferred to register DR the 16-digit binary word which in binary form contains the state of the 16-group of subscribers in question according to the preceding sensing, as it has been described in connection with the FIGS. 2 and 3. The contents of register DR of data memory DMlA is transferred to the register AA of the central unit CE of calculating unit DlA by opening the contact 1/1 and the contents of register FR of transfer unit FElA is transferred to the register AR in the same central unit by opening the contact 3/1. The values are compared in the logical unit LE and if they are equal the address is increased by one, thus carrying out a new operation identical with the preceding one. If, on the contrary, the contents of the two result registers DR and FR are found to be unequal several different possibilities arise: it is possible that a new call has been initiated, a call in progress has been terminated, or dialling is going on. In order to distinguish between these states further digit positions exist in the data memory DMl by means of the contents of which digit positions the computer can calculate whether the actual conductor is connected or is in the state of dialling. For the sake of simplicity it is assumed in this case that it is the question about a new call not yet served, which implies that the subscriber shall be connected to an idle code receiver KM for receiving the digits sent from the subscribers apparatus. The computer formed by the calculation unit DlA and the data memory DMlA is, according to the example, programmed in such a way that it selects a code receiver KM and selects an appropriate path between the subscribers line and this code receiver over idle selectors in the switching network SLGV. In the data memory DMlA is written on one hand the occupied or idle state for all the code receivers and on the other hand the occupied or idle state for all the selectors. Furthermore there exists in the data memory DMlA an information about all the switching paths through the selectors over which a definite subscribers line can be connected to a definite code receiver, and the computer comprising calculating unit DlA and data memory DMlA selects the first idle one of these switching paths. By means of this information which unambiguously determines the selection of paths through the selectors, the establishing of the connection between the calling line and the selected code receiver KM will take place. The establishing of the connection will occur by means of the computer formed by the calculation unit D2A and the data memory DMZA and for this purpose the information concerning the code receiver KM and the selectors is transferred over the contact 5/1 to the data memory DMZA which momentarily forms a computer with unit D1, after which the computer comprising units DlA-DMlA continues to sense the idle or unoccupied state of the lines, the selectors and the code receivers.

The computer comprising units DZA-DMZA whose task is to carry out the establishing of connections through the switching network SLGV arrives, during the carrying out of its instruction list, at an instruction which determines that the contents shall be read out from that field into which the computer comprising units DlA-DMlA writes the information concerning the selectors to be connected. This information is transferred from data memory DMZA to central unit CE of calculating unit DZA over the contact 5/3 and by means of this information the selectors will be set. For the sake of simplicity it is assumed that it is the transfer unit FE2 alone that carries out the connection of the selectors. The connection takes place by means of selector operating relay sets VMR which in their turn are operated by the fast relay operating unit SMR. The central unit CE of the computer comprising units DZA-DMZA must consequently send on the one hand a l6digit binary word to the transfer unit FEZA in order to select a l6-group of operating means one of which shall be activated to connect a selector, and on the other hand a 16-digit binary word in which in the digit position corresponding to the selector to be connected, 1 is found while in the remaining digit positions 0 is found. The first mentioned function is carried out by transferring via the contact 7/3 to the address register FA the address of the respective 16-group in consequence of which via the address decoder A0 a l6-group of operating means is selected in operating unit SMR. The last mentioned function is carried out in such a way that the word which contains the information stating which of the means within the l6-group has to be activated, is transferred to the result register FR, the contact 7/3 is opened after which a writing pulse is sent to the transfer unit FEZA (compare FIG. 2) and the operating means selected in unit SMR operates and connects the intended selector. This operation is of course repeated for every one of the selectors which is included in the switching path in consequence of which the switching path determined by the computer comprising units 1 1 DZA-DMZA from the calling subscriber to the selected code receiver KM is established.

The code receiver shall be sensed so that digit receiving storing and digit analysis can take place. Correspondingly to the distribution of the work earlier mentioned this is carried out by the computer comprising units D3A- DM3A, in the data memory of which all digit information and all information which is necessary for the digit analysis is stored. For causing this computer to sence that a new operation shall be carried out from the moment of connection of a new code receiver KM, the number of the latter and the identity of the established connection must be transferred by means of the unit D2A to the data memory DM3A through the contact 9/3. In the data memory DM3A a special field is reserved for incoming information from memory DMZA. At a later time the calculation unit D3A will, through the contact 9/5, read out the information stored in the special field of memory DM3A after which the signally in the intended code receiver is initiated. The calculation unit D3A causes a sensing of the code receiver KM at regularly running intervals, e.g. every tenth millisecond, in order to find out whether digit information has been received or not. With the presumed simplified distribution of the work between the transfer units the mentioned sensing is carried out by means of the relay test units R'Il of the transfer unit FE3A and the information is transferred through the contact 11/5 to central unit CE of the unit D3A which carries out the reading of the digit signals and then stores the received digit in the memory DM3A through the contact 9/5. The received calling number is stored digit by digit in memory DM3A until the computer unit comprising units D3A-DM3A can establish whether the received digits are sufficient to determine the continued switching path. When this has occurred the computer comprising units BSA-DM3A sends its information to, e.g., the computer unit comprising units DIADM1A in order to select the continued switching path over idle selectors in the switching network SLGV. For this purpose the computer unit comprising units D3A-DM3A writes into a special field of memory DMlA the information which is necessary for the computer unit comprising units DlA-DMlA to carry out a path selection The function in this case is analogous with the function earlier described in connection with transferring of information between memories DMlA and DMZA and between memories DMZA and DM3A respectively.

In this phase the connection of the subscriber with the code receiver KM shall be disconnected after which the calling subscriber shall be connected to an idle connecting circuit SNR and from this the continued connection shall be set up towards the called subscriber if it was the question about a local call. If the called subscriber belongs to another exchange, the calling subscriber shall be connected to an outgoing repeater FUR after interruption of the connection with the code receiver, provided that no digit sending is needed to the following exchange. If on the contrary, digit sending to another exchange must take place, this is determined by the computer unit comprising units D3ADM3A and also in which way the sending of digits shall take place after which a connection is set up between a code sender KS and an outgoing repeater FUR. Even in this case a request is transferred concerning the establishing of connection from the computer unit D3ADM3A to the unit DlA-DMlA in order to carry out a path selection. In all the cases mentioned above the information concerning the selected idle switching path is transferred from the unit DlA-DM1A to the unit DZA-DMZA as it has been described earlier in connection with the establishing of a connection between the calling subscriber and the code receiver KM. If sending of digits to another exchange is concerned, i.e. if a code sender KS shall be connected to a repeater FUR, the information with respect to the identity of the connected code sender KS will be transferred from memory DMZA to memory DM3A. The selected code sender KS can now serve the connection in question by obtaining operation signals from the transfer unit FESA in which the fast relay operation unit SMR is operated by means of the computer unit D3ADM3A. When the digit signalling has been finished a signal is sent to the computer DZA- DMZA so that the connection through the switching network SLGV can be set up via repeater FUR to the outgoing line simultaneously with the disconnection of the connection between sender KS and repeater FUR.

The described operation is illustrated in the FIGS. 4a and 4b in which the telephone plant TA, the transfer units FEl, FE2, FE3 and the computer units D1-DM1, DZ-DMZ and D3-DM3 are indicated in the form of blocks and the transfer of information between the different units is indicated by arrows carrying a number. The number is related to the following numbered functions. In FIG. 4a is indicated the operation of the connection of a subscriber to a code receiver and the establishing of a local call with the guidance of the digit information sent from the calling subscriber:

(l) Sensing of subscribers calls (Dl-FEl).

(2) Selection of an idle code receiver (DI-DM1).

(3) Selection of an idle switching path to the selected code receiver (DI-DM1).

(4) Transfer of the information concerning the idle switching path to the code receiver (DI-DMZ).

(5) Connection of the selected switching path to the code receiver (DM2D2FE2).

(6) Transfer of information concerning the identity of the connected code receiver (D2-DM3).

(7) Sensing of the digit signals and storing (FE3-D3 (8) Transfer of information concerning the switching path interpreted by means of the digit signals (D3- DM1).

(9) Disconnection of the code receiver (DM3-D2-FE2).

(10) Selection of an idle switching path to a connecting circuit relay set (DI-DM1).

(11) Transfer of information concerning the selected switching path (DI-DMZ).

(l2) Establishing of the connection of the selected switching path to the connecting circuit relay set or FUR (DM2-D2-FE2).

FIG. 4b shows the operation of the establishing of a call to another exchange involving the sending of digit signals. The paragraphs l-7 coincide with FIG. 4

(18) Transfer of information implying that a code sender shall be selected (D3-DM1).

(l9) Selection of an idle code sender and of an idle FUR connectable to this code sender (D1DM1).

(20) Transfer of the information concerning the switching path between KS and FUR (DI-DMZ).

(21) Connection of the code sender to FUR (DMZ-D2- FEZ).

(22) Transfer of information concerning the identity of the connected code sender (DZ-DMS).

(23) Sending of digit information (DM3D3-FE3).

(24) Sending of information implying that the digit sending over FUR is terminated (D3-DM1).

(25) Selection of a suitable switching path from the called subscriber to the same FUR (BL-DM1).

(26) Disconnection of the code sender (D1DM2, DMZ- D2-FE2).

(27) Transfer of information concerning the switching path between the subscriber and FUR (DI-DMZ). (28) Establishing of the connection between the called subscriber and FUR (DM2D2FE2).

As it is easy to understand practically every one of the calculation units D1, D2, D3 must have access to every one of the data memories DMl, DMZ, DM3 and to the transfer units FEl, FE2, FE3 in order to write in and read out information. Considering that the calls to the data memories arrive at different times a queue handling system must be found which determines in which sequence the reading and writing instructions, respectively, from the respective calculation units shall be handled. This is indicated in FIG. which shows the three calculation units D1-D3 and only one data memory DM1 and one transfer unit FEl for the sake of simplicity. To the data memory DMl belongs a number of address registers DA1, DA2, DA3 and a number of result registers DR1, DRZ, DR3 in correspondence with every one of the calculation units D1D3 and even the transfer unit FBI has three address registers FAl, FA2, FA3 and three result registers FRl, PR2, PR3. The units DMZ, DM3, FEZ, FE3 which are not indicated in the figure for the sake of simplicity also have three address registers and three result registers. Every one of these registers are, through and-circuits, e.g. OK13 (compare FIG. 2), connected to a 16-wire signal conductor belonging to a definite calculation unit. The address register DA1 is connected to e.g. the signal conductor SL1 belonging to the calculation unit D1 through an andcircuit OK13/ 1, the address register DA2 is connected to the signal conductor SL2 belonging to the calculation unit D2 through the and-circuit OK13/ 2, the address register DA3 is connected to the signal conductor SL3 belonging to the calculation unit D3, etc. Registers with identical index numbers, e.g. DA1, DRl of the three data memories DM1DM3, are connected to the same signal conductor, according to the example conductor SL1, etc. An information which from unit D1 is transferred to memory DMl passes from the signal conductor SL1 through the andcircuit OK13/1 which is opened by the control unit SE of the unit D1 and the information is stored in register DA1. If, on the contrary, an information shall be transferred from unit D2 to memory DMl it passes from the signal conductor SL2 through the and-circuit OK13/2 which is opened by the control unit SE of the unit D2 and the information is stored in register DA2, etc. In a similar way the result of reading out of memory DMl is obtained from the result registers DRI, DR2 and DR3 respectively and can be transferred to the signal conductor of that one of the calculation units which shall use the read out result. This takes place in such a way that the corresponding and-circuit, e.g. OK9/2, if the result shall be transferred to the unit D2, is activated by the control unit SE of the calculation unit D2. The sequence in which the three registers, e.g. DA1, DA2, DA3 are dealt with is determined by means of a sequence governor TU of arbitrary, known type which sequentially and cyclically senses these registers and causes the result to be stored in the corresponding result registers DRl-DR3. If the data memory DM consists of, e.g., a ferrite memory with a definite cycle time of, e.g., two microseconds, a delay of four microseconds is needed in the most unfavourable case before the information is handled in order to clear the calling queue without confusion of the result. It is easy to see that FIG. 5 is equivalent to FIG. 2 but with the difference that naturally there is a signal conductor SLI-SLU for every unit D and the number of and-circuits 0K8, 0K9, etc. has increased in correspondence with the number of signal conductors in order to make it possible for information to be fed from every unit D to every unit DM and unit FE, respectively, and inversely.

The fundamental idea of the invention is to bring about a redistribution of the tasks in an arrangement of the above described type if the traffic conditions or faults should prevent certain program sections from being carried out within a time interval defined as normal. In a computer controlled telephone system the instruction list of the computer includes a great number of instructions in which different groups or sections concern the different operations which shall be carried out by the computer, e.g., sensing of the state of subscribers lines, operation of selectors. storing of impulses, etc. If the computer should carry out the instructions concerning a certain type of function, e.g. sensing of subscribers, disregarding that the remaining operations, e.g. connection of selectors, digit impulse receiving etc., are waiting, the next operation would never be initiated or initiated only when no work concerning said certain type of function is found, e.g. when no call has been done. The operations which are to be carried out in a similar system, have, however, different degrees of urgency and are divided up into, e.g., three categories A, B and C the first mentioned of which has preference over the second and the second over the third as it will be explained in connection with FIG. 8. Furthermore every one of these categories includes a plurality of different operations which among themselves have the same priority. For the mentioned reason a supervisory program is necessary which determines on the one hand for how long a certain program section can go on, and on the other hand which priority level or which operation of this priority level shall continue after the conclusion of a program section. The supervisory program intervenes consequently, e.g., if an operation of lower priority level has been dealt with too long a time, it brings about storing of the tasks of the program section going on and starts a section with a higher priority level or determines that a section shall be completely omitted etc.

In an arrangement in which a plurality of computers serves a telecommunication system the conditions become more complicated in that the different computers divide up the operations among themselves. As earlier mentioned the instruction sequence for every computer in such a system can include all the instructions, i.e. all the program sections which are necessary in order to make it possible for one computer alone to serve the whole plant but every one of the computers carries out only a part of the tasks. For the mentioned reason the supervisory program which controls the programs of the individual computers includes only those sections which shall be carried out by the respective computer. The addresses of these program sections are recorded in a special field but they can be exchanged for other program sections in order to allow a rearrangement of the tasks between the different computer units. This takes place by means of a second supervisory program which to distinguish from the above mentioned program, the computer supervisory program, this is called system supervisory program. This will first be explained in general outline with the aid of FIG. 6. This figure shows two calculation units D1, D2 and two data memories DMI, DMZ which form computer units D1 DM1 and D2-DM2. Each one of the data memories has an indicating memory field IF in which information is recorded, e.g. in the form of 16-digit binary words concerning the address of the sections of the instruction sequence, which shall be carried out by the respective calculation units. To the calculation unit belongs a field KMO, suitably in the instruction memory IM this field which stores the computer supervisory program determines the initiation of the different program sections in the instruction sequence as it will be explained in connection with the FIGS. 7-9. After the conclusion of a section of the instruction sequence corresponding to an address word recorded in the indicating memory field IF, the next word is read out in field IF and with the guidance of this word the next instruction section is carried out until the whole field has been scanned. The computer supervisory program KMO will take care of, inter alia, not only that the program sections recorded in field IF are carried out in the recorded sequence but also that on the one hand only such sections in the instruction list are passed through in which work is found and on the other hand the sections are treated during a predetermined time period. This will appear from the FIGS. 7-9.

As long as the system functions normally, i.e. no fault appears in the circuits or the individual program sections generally are terminated within a time interval which is defined as normal, there is no reason for changing the working list recorded in the indicating field. It can occur, however, that the time intended for the handling of a definite program section is exceeded which is established by the computer supervisory program and a signal is obtained as it will be explained later on. A fault can be signalled even as a consequence of a deviation between the information found in the redundant computer units in a known way. These signals cause, according to the signification of the signal, the start of different program sections of a system supervisory program which, according to the example, is also recorded in a special field SMO in the instruction memory IM in order to remedy the fault. As indicated symbolically in FIG. 6 each one of the calculation units D1, D2 includes a field SMO for a system supervisory program and the calculation unit in which abnormal conditions are indicated can, by means of the system supervisory program, read out the indicating memory field IF, erase parts of this and carry out new recordings in order to change the subsections which shall be handled. The calculation unit can carry out these operations, not only in the indicating field IF with which it normally cooperates, but even in the indicating field of the other calculation unit. Upon the receiving of a fault signal or a signal which indicates abnormal working conditions the system supervisory program makes an analysis of the type of the fault possible so that at first hand the effect of the fault can be minimized. In the most simple case, e.g. momentary overload, it is possible, e.g., by means of the system supervisory program to erase one or more section addresses in the field IF of memory DM. In the case when the operating time of a job with a lower urgency grade is exceeded within a limit allowed by the programming, the system supervisory program does not need to function but passing to another task can take place by means of the computer supervisory program as it will be explained in connection with FIG. 9. The fault can, however, be of such a complicated type that it is no longer possible to eliminate the overload only by erasing a few unessential sections of the working list. On this case the system supervisory program accomplishes that such sections which not simply can be erased from the indicating field of an overloaded computer are erased but transferred to the working list of the indicating field of another computer which for the moment has capacity available. This will be explained more in detail in connection with FIGS. lll3. It is even possible that the content of a data memory can be erased and transferred to a stand-by data memory in a similar way in the case a data memory is faulty.

FIG. 7 shows diagrammatically how the program of the computer, recorded in the instruction memory, is controlled. This occurs by means of the machine supervisory program recorded in a memory field KMO, and by means of a work list recorded in another memory field, herebelow called indicating field. One or both of the fields KMO and IF can be located in the instruction memory IM or in the data memory DM and their positions have no importance from the point of view of function. For the sake of simplicity it is assumed that the whole system comprises only two calculation units D1 and D2, two instruction memories 1M1 and 1M2 and two data memories DM1 and DM2. Both instruction memories include all program sections necessary for the work of the telephone exchange but every calculation unit carries out only part of the whole program. This is indicated in FIG. 7 in such a way that every program section recorded in the instruction memory IMl which program section is treated by the computer formed by the calculation unit D1 and the data memory DMl, has the index 1 while those sections which are treated by the calculation unit 2, have the index 2. The work list of the indicating field IF includes sequentially the addresses of those program sections of the instruction memory which are to be treated by a certain calculation unit. According to this example it has been assumed for the sake of simplicity that the addressscs of all program sections which are to be treated by the calculation unit D1, are recorded in the indicating field IFl although it also is possible that some of the addresses are recorded in the indicating field IF2.

In the indicating field IFl the addresses of the different program sections in instruction memory 1M are recorded in that numerical sequence in which they are to be treated by the calculation unit D1. If it is assumed that the address of a certain program section in instruction memory IM has been read out from indicating field IFl at a definite moment, the handling of this program section will start according to the instructions recorded in the section. When the last instruction of the program Section has been performed, the operation of the next program Section will not continue but that section is selected as next whose address is next in the indicating field IF. The address of that word in the field IF which includes the address of the just concluded section is recorded in the field KMOI which includes the machine supervisory program, so that after increasing this address by 1 the next section address in instruction field IF can be selected. This process will be elucidated in connection with FIG. 7 which also shows how a section is jumped over when there is no work in that section. In FIG. 7, for the sake of simplicity, no regard has been paid for the present to the fact that the work going on in a certain section must be interrupted periodically and be replaced by a section with a higher priority level if the traffic conditions make this necessary, as will be explained below in connection with FIG. 8 and it has been assumed that the work is controlled only by the work list in the indicating field IF.

In FIG. 7 the difierent processes, i.e. feeding in-and feeding out of information to and from the different memories, IFl, lMl and KMOl and to and from the central unit CEl are indicated by arrows and every arrow is provided with a number indicating the order in which different stages succeed each other. As has been mentioned earlier the addresses of those sections in the instruction memory IM which are to be treated, are recorded in the indicating field IFl. It is presupposed that at a definite moment the central unit CEl reads out the contents of the word Wf3 in the indicating field IFl which word indicates the address of section 3/1 in the instruction memory 1M1 (the arrow 1). By means of this address the first word Wrl in the section 3/1 of instruction memory IMl (2) will be read out. This first word Wrl indicates in its turn the address (3) of the first word Wkl in the field KMO of the supervisory program that is associated with the section 3/1. This word Wkl includes on the one hand the address of word Wf3 in the indicating field, on the other hand an information concerning the priority level of section 3/1 and also the address of a priority level indicating word Wnl in field KMO which word includes information concerning the priority level of the preceding section. (The meaning of the expression priority level" will be explained in connection with FIG. 8.) The word Wkl is read out for selection of the Word Wnl (5) and is transferred to the central unit (4) to which also the contents of the word Wnl (6) is transferred in order to compare the priority level of the earlier treated section with the priority level of the present section. If they are equal, no change in the record in word Wnl will be necessary but the word Wpl in field KMOl is selected (7a) into which word in an earlier phase has been written whether work exists in section 3/ 1. If the priority level information were different, first a change of the record in Wnl will be necessary (7b), besides the selection of the word Wpl. In case the word Wpl upon the reading out (8) has indicated that there is work to carry out in the section 3/ 1, the next word WrZ in the instruction sequence in memory IMl (9a) will be read out which word is a common instruction word in the instruction list of the computer. When this instruction is concluded the next instruction 

